Protection from malware on a Linux “desktop”There are tons; at the moment this question is basically answered by googling "linux antivirus". If you have a specific problem that's something we can help with, but "how can I prevent all malware" is too broad

How to create a script that can't be easily exitedDo you want to prevent interrupts from killing a script, or do you want to prevent users from canceling the update? The latter is more general and has simpler solutions, so you're going to end up getting answers for that even if you asked for the former

SUID accidently removed from /bin/su fileYou can't just make your own copy of su and expect it to work; that'd be pretty alarming if you could. The standard su is owned by root and setuid so it runs as root